1. Field of the Invention
This invention relates to 3rd Generation (3G) mobile communication system, especially to a method for SGSN to distinguish MBMS service request from other service requests.
2. Description of the Related Art
MBMS is a new service under standardization by 3rd Generation Mobile Communication System Partnership Project. The MBMS service is an unidirectional point-to-multipoint (p-t-m) (i.e. multimedia data sent from a single data source is transferred to multiple users through network transmission) service. Most remarkable feature of the service is that it can make use of radio resources and network resources efficiently. The MBMS service is mainly used in wireless communication network system, e.g. Wideband Code-Division Multiple Access system, Global System of Mobile Communication, etc. The transmission of the MBMS service data basically includes following several steps, i.e. data source sending, middle network transmission, destination cell on-the-air transmission and user reception. FIG. 3 is a logical figure for network devices of the radio communication system that can provide the MBMS service, in which the MBMS actually makes use of General Packet Radio Data Service (hereinafter referred to as GPRS) as core transmission network. As shown in FIG. 3, Broadcast and Multicast Service Center (hereinafter referred to as BM-SC) is the data source for the MBMS data transmission. Gateway GPRS Supporting Node (hereinafter referred to as GGSN) is used to connect the GRPS network with the external network (such as INTERNET). Gateway GPRS Supporting Node is used to connect BM-SC in the MBMS service and to send MBMS data to specific Service GPRS Supporting Node (hereinafter referred to as SGSN). Cell Broadcast Center (hereinafter referred to as CBC) is the data resource of the cell broadcast, through interconnecting the CBC with the BM-SC in the MBMS, the CBC can provide the MBMS service with declaration function. The SGSN is used to perform access control on a UE as well as mobility management, and sends the MBMS data from the GGSN to the specific Radio Network Controller (hereinafter referred to as RNC) at the same time. The RNC is used to control a group of base stations (hereinafter referred to as NODE B) and sends multimedia data to the specific NODE B. The NODE B (base station) establishes air physical channel for the MBMS service in a certain cell under the control of the RNC. Terminal User Equipment (hereinafter referred to as UE) is the terminal equipment for MBMS data reception.
FIG. 4 gives the whole process from service announcement, user joining, service notification, radio bearer establishment to user's final leaving in the MBMS service.    401 Subscription—establishing the connection between a user and a service provider, and an authorized user may receive the relevant MBMS service.    402 Service announcement—notifying the user of services that will be provided. For example, the system will rebroadcast a football match in Beijing at 7:00 p.m.    403 Joining—indicates that the user joining a group, i.e. the user informs the network that he or she is willing to receive this multicast service.    404 MBMS Session Start—indicates that establishing the network resources for the MBMS data transmission.    405 MBMS notification—indicates that notifying the user of the MBMS data transmission that will be performed right away.    406 Data transmission—indicates the process of transferring the MBMS service data to the user.    407 MBMS Session Stop—indicates that releasing the network resources after the MBMS data transmission is completed.    408 Leaving—corresponding to the joining of 403, which indicates that the user is leaving a group, i.e. the user doesn't want to receive the data of a certain service any more.
In WCDMA system, the system requires each UE to enter the connection state of PMM_CONNECTED when providing conventional packet service for the UE. This state indicates that there is radio resource control (RRC) connection between the UE and the UTRAN, and there is signaling connection between the UE and the SGSN. The signaling interchanged between the UE and the SGSN belongs to Non-Access Signaling, i.e. NAS signaling. This signaling is transparent to the RNC, that is, the RNC doesn't care about the content of the message transferred between the UE and the SGSN. When the UE wants to enter the state of PMM_CONNECTED to establish the signaling connection, it must send the SERVICE REQUEST message or the ROUTING AREA UPDATE REQUEST message to the SGSN. The ROUTING AREA UPDATE REQUEST message is only needed when the UE wants to update its routing area. The SERVICE REQUEST message is used to establish the signaling connection between the PMM_IDLE UE and the SGSN, and to tell the SGSN for what the message transfers, i.e., for transmitting uplink signaling message, uplink data or responding to the paging from the CN. If the service type in the SERVICE REQUEST message is signaling, the SGSN will release the signaling connection between RNC and SGSN after the process of signaling exchanging completes; if the service type in the SERVICE REQUEST message is data, the SGSN will establish the Radio Access Bearer (RAB) for the service in active state so as to establish the Radio Bearer for transferring data for this service; if the service type in the SERVICE REQUEST message is paging response, the SGSN knows whether this paging response aims at data transmission or signaling exchanging so as to make a correct decision to transfer relevant signaling to the user equipment or to establish the RAB. To provide the MBMS service in the WCDMA system, if all users that receive the MBMS service are in PMM_IDLE state, it is possible that a lot of radio resources be used or wasted in the on-the-air interface, for large amount of users are sharing MBMS service at this time. In this case, the method that let part of the user equipments be in PMM_CONNECTED state and the rest be in PMM_IDLE is adopted in UTRAN. Therefore, the Radio Network Controller needs to count the users in PMM_CONNECTED state in its cells only. The reason why the user equipment stays PMM_CONNECTED state is either that this user equipment is receiving other dedicated service or only for MBMS user counting. Once the RNC finds out that the number of user equipments receiving MBMS service in a certain cell is less than the threshold on switching between the channel of point-to-point and point-to-multipoint, it will recount it so as to prevent that some other user equipments in PMM_IDLE state in this cell are still receiving MBMS data. Referring to FIG. 5 for more information on this process. 501 indicates that the RNC receives the message of “Session Start Indication” from the SGSN, which means the start of MBMS session, and this message generally includes service parameters related to the service, such as Service ID, QoS parameters, etc. The RNC counts the number of UEs that subscribe the service in each cell. This process is mandatory at the beginning of the session. And during the session, if the number of UEs is lower than the threshold on switching from the point-to-multipoint (PTM) to the point-to-point (PTP), then the RNC will start the process of counting the number of UEs. This process continues from 502 to 512. If the RNC finds that the number of UEs is lower than the threshold, then the RNC sends a “MBMS Notification” message to the UE in PMM_IDLE state or maybe also to the UEs in the states of CELL_PCH and URA_PCH. This message includes parameters such as notification reason (MBMS called-party calling), access probability and service ID, etc. The UE in PMM_IDLE state first establishes a RRC connection with the RNC after receiving this message. From 504 to 506, the UE establishes the RRC connection with the RNC, which is consistent with the process described in existing specification, and the unique difference may be the reason for the RRC connection establishment. This reason may be “MBMS called-party calling”. The NAS layer of UE sends a “Service Request” message to the SGSN. This service request message is delivered to the SGSN in the 507 RRC message “Initial Direct Transmission” and the 508 Iu signaling “Initial UE Message”. When the SGSN receives this message, it sends a message of 509 “MBMS UE Linking Request” to the RNC to deliver all MBMS service IDs that the UE subscribes to the RNC. The RNC returns the message of 510 “MBMS UE Linking Response” back to the SGSN. 511 the RNC adds this UE ID to each service context of the cell that the UE stays in. 512 the RNC counts the number of UEs in each cell. Thus, the process of counting the number of the UE by the RNC is completed.
In the SERVICE REQUEST message sent by the UE to the SGSN, if the service type in the Service Request is data, then the SGSN establishes the RAB for the activated PDP Context, so that the resource allocation is performed on Iu and Uu interface for data transmission. During the process of MBMS UEs counting, when the UE receives the message of “MBMS Notification” from the RNC, if the message indicates that the number of UEs needs to be collected, then the UE will enter the PMM_CONNECTED mode. The UE in PMM_IDLE state sends the “Service Request” message to the SGSN to enter the PMM_CONNECTED mode. If the service type in the service request at this time is also data, then according to the prior art, the SGSN needs to establish the RAB for the activated PDP Context. However, this service request actually aims at the MBMS service and the UE hasn't requested for data transmission of the dedicated service. It shows that faulty operation may be induced on the SGSN. In order to avoid the faulty operation on the SGSN, we propose to add a new service type, i.e. MBMS service, to the service request. Also we can use a new message, i.e. “MBMS Service Notification” to inform the SGSN that the MBMS service subscribed by the UE should be known to the RNC, i.e., the MBMS UE Linking Request shown in FIG. 1.
In the WCDMA system, there is another case in which the UE switches into the PMM_CONNECTED state without transferring the SERVICE REQUEST message, i.e., the case when the UE switches into routing area update. In this case, if we want to have the SGSN notify the RNC of the MBMS service that the UE joined in, we can add an information unit of “MBMS Indication” in the message of “Routing Area Update Request”. Also, we can adopt the new message “MBMS Service Notification” to request the SGSN to transfer the MBMS service subscribed by the UE to the SRNC of the UE.